The replacement XT Measuring Heads are only compatible with Fowler/Bowers XTH Pistol Grip Bore Gages, XTA Analog Holemikes and the XTD Electronic Holemikes. Any XT measuring heads above .250"/6mm being offered by www.boregages.com will not be compatible with older generations of the Fowler/Bowers bore gage sets. If you are looking to replace any parts or anvils on an XT head your company already has, it is best to contact one of our inside sales representatives for assistance.